Low-speed Wire Electrical Discharge Machining Research Articles

Enhancing low-speed WEDM machining capabilities on Nitronic-50 with a constant frequency ultrasonic hybrid method

Nitronic-50 stainless steel is a high-strength and corrosion-resistant austenitic premium steel. It requires improved surface characteristics due to its wide use in various applications like fasteners, marine hardware, hydroelectric-power turbines, pressure vessels, etc. This work focuses on machining hard-to-machine Nitronic-50 steel is unconventionally machined using constant frequency ultrasonic-aided low-speed wire electrical discharge machining (USV-LS-WEDM) to enhance its machined surface integrity. This method achieves effective results when cutting high-strength materials with intricate shapes. Material removal rate (MRR) and surface roughness (Ra) were measured by considering inputs such as servo voltage (SV), pulse off time ( Toff), pulse on time ( Ton) and current (I) with an ultrasonic-vibration range of 20,000 Hz. The appropriate selection and usage of LS-WEDM parameters is a challenging process and is done with parametric analysis. The MRR of Nitronic-50 was enhanced with an increase in Ton and I along with a reduction in Toff and SV. Surface roughness (Ra) decreased with a gradual reduction in Ton, I, and an increase in SV. The USV-WEDM was compared with a stand-alone WEDM indicating that the MRR for USV-WEDM was improved by 12% and the Ra was decreased by 9% due to effective distribution of spark discharges, which increased material erosion and redistribution of molten metal characteristics. Machining quality for hard-to-machine Nitronic-50 steel was certainly enhanced via hybrid ultrasonic vibration with the existing LS-WEDM.

Test and Improvement of a Fuze MEMS Setback Arming Device Based on the EDM Process.

This paper introduces the working principle of a MEMS safety and arming (S&A) device for a fuze that is installed perpendicular to the axis of the projectile. Additionally, the application of low-speed wire electrical discharge machining (EDM) in the fabrication of the device is proposed. Microsprings are susceptible to flexural deformation and secondary deformation in the EDM process, a problem that is solved by designing the auxiliary support beam, using multiple cuts, destress annealing and optimizing the processing parameters. The difficult problem of setback slider deformation in the principle prototype test is properly solved by establishing V-shaped grooves at both ends of the setback slider. The connection mode between the microspring and the frame is changed to a clearance fit connection. The improved setback arming device can guarantee service process safety and launch reliability. The maximum overload that can be withstood in service processing is 20,000 g, and the minimum overload for safety release during launch is 12,000 g. The results show that the EDM process can greatly reduce the machining cost while improving the machining precision and machining speed, which can compensate for the defects of the current manufacturing technology.

Ultrasonic injection molding of glass fiber reinforced polypropylene parts using tungsten carbide-cobalt mold core

A hybrid process combining ultrasonic injection molding and electrical discharge machining was proposed to realize the economic, high-precision, and environmental-friendliness production of glass fiber reinforced polypropylene microstructured parts. First, the prism array microstructures were processed on tungsten carbide-cobalt (WC-8 wt% Co) substrate by low-speed wire electrical discharge machining and used as the mold core. Then, the glass fiber reinforced polypropylene composite (GF/PP) was melted under ultrasonic vibration, and the surface microstructure of the mold core was replicated. The experimental results show that this method can efficiently and accurately manufacture microstructured parts, and the microstructure has a high replication rate up to 95.5%. By replicating the microstructure, the surface contact angle of GF/PP parts increased from 57.1° to 134.9°, and the wettability changed from hydrophilicity to hydrophobicity. The mechanical properties test results show that the GF/PP parts fabricated by ultrasonic injection molding had excellent mechanical properties, and the 30% GF/PP parts show the highest tensile strength of 56.9 MPa. This work provides a new option for fabricating fiber reinforced composite parts.

Study on surface characteristics in ultrasonic vibration-assisted WEDM-LS based on spatial vibration of electrode wire

The spatial vibration model of the electrode wire in ultrasonic vibration (USV)-assisted low-speed wire electrical discharge machining (WEDM-LS) under continuous discharges is proposed for analyzing its vibration state, and subsequently, a theoretical model of material removal from the TiNi-01 shape memory alloy workpiece is established by means of Gaussian heat source in single-pulse discharge process and the principle of the nearest-point discharge breakdown. Then, the topological matrix of the surface morphology is developed for investigating the surface characteristics and the distribution of discharge points by simulation. Finally, the experiment of photographing the discharge channel position is accomplished to validate the reliability and feasibility of the model. The results show that the discharge channels are more uniformly distributed in the hybrid process, which enhance effectively the success rate of the discharge pulses and decrease the surface roughness. In addition, a mathematical model to evaluate the uniformity of the discharge point distribution is employed as an evaluation index of the burn degree on the workpiece surface. The distribution uniformity coefficient obtained by the compound process is higher than that of the traditional WEDM-LS. This is consistent with the phenomenon of alleviated surface burn under the hybrid machining technology, and the average errors of the simulated and experimental values of the uniformity coefficient of traditional WEDM-LS and the hybrid process are 4.9% and 3.4%, respectively. The maximum errors of surface roughness between simulated value and experimental value about the WEDM-LS and hybrid process are 7.4% and 8.2%, respectively. It is demonstrated that the model can effectively and accurately predict the surface roughness and the surface burn of the workpiece.

Investigation on the kerf and surface formation in the magnetic field-assisted WEDM-LS based on successive discharges

Magnetic field-assisted low-speed wire electrical discharge machining (MF-assisted WEDM-LS) is an effective technique to improve the surface quality of the workpiece. This paper presents a successive removing model to predict kerf width and the surface topography of nickel–titanium (Nitinol) shape memory alloy in different parameters. Firstly, the motion of an electron was calculated in the magnetic field. It could be obtained that if the length of the discharge channel path was the same with the condition that in traditional WEDM-LS, the width of the discharge gap was decreased because of the deflection of the electron trajectory caused by the magnetic field. Then, a modified gauss heat source equation was derived by calculating the incident angle of the discharge channel. Based on the principle of conservation of energy, the shape of the crater in different parameters was emulated. Moreover, an electrothermal coupling model was established to investigate the surface formation in the successive discharges process. The simulation results show that the average value of the surface roughness of the workpiece in WEDM-LS with magnetic field assisted was decreased by 12.3% compared with that in traditional WEDM-LS. Eventually, experiments of kerf and surface quality were carried out respectively. The experimental results showed that the kerf decreased from 376.2 to 361.7 μm in the magnetic field intensity of 0.4 T. The surface topographies of the workpieces showed good agreement with the simulation results, and the average relative error of surface roughness between simulated results and experimental results is 8.7%.

Machining of cylindrical parts by wire electrical discharge grinding using thin plate guide

In order to meet the processing requirements of precise cylindrical parts on hard and difficult-to-machine materials, this paper introduces wire electrical discharge grinding (WEDG) using thin plate wire guide for cylindrical parts machining. The spindle system and the wire transport system to realize this processing method was added to a low speed wire electrical discharge machining (LS-WEDM) machine tool. In order to realize the online measurement of the machining accuracy of the cylindrical parts, an online measurement system of two-degree-of-freedom based on laser displacement sensor was built. The reasons for the incomplete removal of the machined surface were analyzed. Through the application of a new tool setting strategy and reasonable selection of processing parameters, the phenomenon of incomplete processing can be avoided. The experimental research on the effects of part rotational speed, wire feed rate, wire running speed and wire tension on roundness, surface roughness Sa, and surface morphology were carried out. Finally, example of the cylindrical parts is given to verify the machining accuracy.

An experimental study on fabricating microstructured surface by using LS-WEDM-prepared ball micro end mills

In recent years, there is an increasing demand for fabricating microstructures such as micro grooves, micro holes, micro dimples, and micro channels on various materials. Micro machining is an alternative method to manufacture microstructures due to its high efficiency and flexibility, and the micro end mill preparation is an essential step. In this study, the low-speed wire electrical discharge machining (LS-WEDM) is used to fabricate ball micro end mills with four cutting edges and radius of less than 200 μm, and the optimized parameters and multiple cutting strategies are adopted to improve machining surface quality and edge sharpness of ball micro end mills. Then, the micro dimples on soft and hard materials are formed by the designed and prepared ball micro end mills made of cemented carbide, respectively. The micro machining performance of ball micro end mills was evaluated by investigating the surface quality and microstructure of micro dimples, cutting force, and tool wear, and the influence of micro machining parameters on micro dimples is discussed in detail. Experimental results indicated that tool wear patterns mainly are adhesion friction and cutting edge damage, and the LS-WEDM-fabricated ball micro end mills with four cutting edges are potential to manufacture microstructures on hard and soft materials with acceptable surface quality and tool wear.

Experimental study on fabricating ball micro end mill with spiral blades by low speed wire electrical discharge machining

This study is focused on developing and fabricating ball micro end mills with spiral blades by using low speed wire electrical discharge machining (LS-WEDM). Firstly, the new type ball micro end mill is designed and the mathematical model of wire movement trajectory is established for optimizing machining parameters and realizing visual prediction. Then, the diameter, spiral width, and the length consistent accuracy of ball micro end mills fabricated by LS-WEDM is investigated in detail, and more importantly, the three-spiral blades ball micro end mill with the diameter of about 278 μm and the length of 1860 μm is firstly and efficiently manufactured by LS-WEDM. Besides, the micro machining performance and tool wear of LS-WEDM fabricated ball micro end mill are evaluated by conducting micro milling experiments on nickel-based single-crystal superalloy DD5 material, and experimental results revealed that the main tool wear of the new type ball micro end mill is friction wear and adhesion wear rather than diffusion wear. Furthermore, the surface roughness of machined surface can be reduced to 183 nm, which indicates that the ball micro end mills with spiral blades fabricated by LS-WEDM are significantly potential to achieve high-quality machining for complex micro structures on hard material.

Study on workpiece surface forming mechanism by successive discharges during USV-MF complex–assisted WEDM-LS process

Ultrasonic vibration and magnetic field complex–assisted techniques have been used in low-speed wire electrical discharge machining (USV-MF complex–assisted WEDM-LS) to improve workpiece surface quality. In this paper, a novel approach, which is based on a three-dimensional successive discharge model, is proposed to investigate the interaction between the workpiece surface forming and the vibration of a wire electrode. The influence of USV-MF complex–assisted technique on workpiece surface forming and vibration of a wire electrode is considered by modifying the parameters in this model. During the simulation, the discharge location, which is determined by the minimum gap width in each step, makes it possible to calculate the vibration of a wire electrode in the successive discharge process. Workpiece surface topographies are obtained at the end of simulation, as well as the vibration responses of the wire electrode and the distribution of discharge locations. The simulation results show that the USV-MF complex–assisted technique can increase the vibration amplitude of the wire electrode by 1.12%. The surface roughness values decrease more than 10% and the distribution uniformity of discharge location increases in the USV-MF complex assisted WEDM-LS process. The simulation results are verified by experiments and simulation error of surface roughness value is less than 5% compared with the experimental results. The analysis shows that the servo feed speed increases more than 50% with surface quality unaltered in the USV-MF complex–assisted WEDM-LS process.

Fabrication of microplastic parts with a hydrophobic surface by micro ultrasonic powder moulding

Microstructures with hydrophobic surfaces have been widely used in industrial fields such as self-cleaning and drag reduction. With the aim of fabricating microplastic parts with a hydrophobic surface, the paper processed the mould insert with micro-groove arrays from 304 stainless-steel plate through low-speed wire electrical discharge machining (LS-WEDM). And the micro-groove arrays were designed to U shape with bottom radius of 70 μm and depth of 110 μm. Ultra-high molecular weight polyethylene (UHMWPE) powders were used as raw material to fabricate microplastic parts with hydrophobic surface structures by micro ultrasonic powder moulding (micro-UPM). The parameters of the micro-UPM process were obtained by the single-factor test method. Under the ultrasonic energy of 1200 J, welding pressure of 100 kPa and pressure holding time of 8 s, microplastic parts with well surface morphology (Ra =1.36 μm) and replication rate (97.76 %) were successfully fabricated. The surface contact angle of the microplastic part was 135.4°, which indicated well surface hydrophobicity.

Optimization of a Fuze MEMS Setback Arming Device Based on the EDM Process

This paper introduces the working principle of a MEMS safety and arming (S&A) device and measures and tests a setback arming device. To solve the problem of large fabrication errors in the UV-LIGA process, a MEMS S&A fuze device fabricated by low-speed wire electrical discharge machining (EDM) is proposed. Microsprings are susceptible to flexural deformation and secondary deformation in the EDM process, which is solved by setting the auxiliary support beam, using multiple cuts and destress annealing. The linewidth, thickness and elastic coefficient of the microspring fabricated using the EDM process are closer to the designed values than those fabricated using the UV-LIGA process under the same conditions. When comparing the MEMS S&A devices fabricated by the two processes, it is found that the EDM process has a the higher machining accuracy. In view of the plastic deformation of the upper end of the microspring, the structure of the microspring is optimized to incorporate a gradient linewidth, and the optimized setback arming device is tested. The results show that the device can ensure service process safety and launch reliability. The maximum overload that can be withstood in service processing is 17000 g, and the minimum overload for insurance release during launch is 1500 g.

Micro milling characteristics of LS-WEDM fabricated helical and corrugated micro end mill

Micro milling offers a high potential for fabricating three-dimensional micro structure, such as micro grooves, micro channels and micro dimples. However, the fabrication of solid micro end mills with hard materials and complex structures poses many challenges. In this study, a new method based on low speed wire electrical discharge machining (LS-WEDM) is presented to prepare solid helical micro end mills. The machining process of helical micro end mill is kinematically modeled and simulated, which can realize visual predictability and provide theoretical basis for parameters selection. Experimental results indicated that corrugated micro end mill with about 269.8 μm in diameter and 1850.2 μm in length, and three helical blades micro end mill with 123.8 μm in diameter and 800 μm in length, six spirals and varied helical angle micro end mills can be flexibly prepared. Furthermore, the use of these micro end mills in hard material of DD5 single crystal nickel-based superalloy substrates is described to demonstrate their potential. Thus, the technique proposed in this study is significantly contribute to the fabrication of complex solid micro end mills with helical blades.

Design of superhydrophobic pillars with robustness

Superhydrophobic surfaces have huge applications in wetting fields. However, compared with natural biological surfaces, artificial superhydrophobic surfaces still show serious deficiencies in the theoretical design and durability. In this work, a robust superhydrophobic surface consisting of a regular array of square pillars with secondary structures on the sidewalls was prepared using low-speed wire electrical discharge machining. We developed the design criteria of regular arrays of square pillars for achieving superhydrophobicity based on interface characteristics and force balance. A series of samples were also prepared to validate the design criteria. The results indicate that the overlap part between the theoretical superhydrophobicity region before and after abrasion leads to stable superhydrophobicity. In addition, specific surfaces transform from the Wenzel state to the Cassie state after abrasion and the contact angle shows a large increase. The design criteria based on the research of predecessors are useful to design superhydrophobic surfaces with robustness.

Experimental study on surface quality and machinability of Ti-6Al-4V rotated parts fabricated by low-speed wire electrical discharge turning

This paper firstly focused on analyzing the characteristics of surface damage in low-speed wire electrical discharge machining (LS-WEDM) and introducing the multiple cutting strategy into the LS-WEDT to improve the surface quality and minimize surface defects. Surface and sub-surface damages of Ti-6Al-4V (TC4) workpiece produced in LS-WEDT are discussed, which includes craters, cracks, surface alloying, surface composition, micro-hardness, and white layer. Experimental results indicated that the craters produced in LS-WEDTed surface are extended and very shallow. Although TC4 material has poor thermal conductivity, cracks can completely disappear by decreasing peak current in LS-WEDT, which differs from LS-WEDM. Comparing with LS-WEDMed surfaces, debris adhering on LS-WEDTed surface is very few due to good flushing condition and point contact discharge mechanism. The foreign elements of oxygen and copper are detected on LS-WEDTed surface, but the contents are less than LS-WEDMed surface. The micro-hardness of the heat-affected zone is much lower than substrate and the discontinuous white layer is obtained in LS-WEDT. The LS-WEDTed surface machined after finishing trim cut (FTC) is very smooth with invisible craters, and the white and heat-affected layers’ thickness are greatly reduced. Finally, practical machining is carried out via fabrication of the rotated micro-part and taper pin with diameter of 40 μm.

Formation mechanism of surface topography in low-speed wire electrical discharge machining Inconel 718 and its on-line prediction based on acoustic emission technology

The mechanism of surface topography formation of Inconel 718 in low-speed wire electrical discharge machining was studied, and its on-line prediction based on acoustic emission detection technology is carried out. An optimized truncated cone-shaped thermal conduction model considering the scattering velocity difference between electrons and ions was put forward. Based on this model, discharge craters and temperature variation at different discharge energy conditions were systematically discussed in finite element analysis. Experimentally, five machining regimes that are reduced in accordance with the discharge energy were conducted with acoustic emission detection technology in low-speed wire electrical discharge machining. A novel denoising method has been proposed, which combines filtering analysis and Fast Fourier Transform. The experimental results indicate that acoustic emission testing technique provides great technical support in researching the discharge energy variation rule in low-speed wire electrical discharge machining. It is also concluded that the change trends of the theoretically calculated temperature in the discharge channel and acoustic emission signal root mean square and the surface roughness value and the acoustic emission signal root mean square show a similar exponential growth law. A regression equation about the arithmetic mean roughness ( Ra) values and root mean square values of acoustic emission is established to predict surface roughness value Ra whose error is less than 1%.

Erratum to: Modeling and experimental study on breakdown voltage (BV) in low speed wire electrical discharge machining (LS-WEDM) of Ti-6Al-4V

In this study, the breakdown voltage behavior in low speed wire electrical discharge machining (LS-WEDM) of Ti-6Al-4V (TC4) in the deionized water is investigated. Firstly, the electric field distortion caused by impurity particles including TC4 or brass metal and bubbles is investigated. And then the breakdown voltage model of TC4 machined by LS-WEDM is established and the experimental verification result indicates that the model predicting results conforms to the actual processing and could be well follow experimental results. Second, the influence of breakdown voltage on surface roughness and kerf width has been revealed, it can be found that the kerf width decreases, and the surface roughness increases as breakdown voltage increased. Besides, the voids become bigger and the surface cracks become deeper and wider with the breakdown voltage increased based on analysis of experiment results but for microcracks distributed on spherical or irregular attachments are not influenced by breakdown voltage due to their randomness. Meanwhile, the transparent bubbles of diameter of 400 nm can be observed near the droplet on the machined surface and its major composing element is oxygen. Finally, internal voids can be found in the joint of deterioration layer and the substrate which will make the combination of deterioration layer and the substrate not strong and easy to fall off.

Modeling and experimental study on breakdown voltage (BV) in low speed wire electrical discharge machining (LS-WEDM) of Ti-6Al-4V

Modeling and experimental study on breakdown voltage (BV) in low speed wire electrical discharge machining (LS-WEDM) of Ti-6Al-4V

Experimental study on accuracy and surface quality of TC2 in LS-WEDM multiple cuts

Low-speed wire electrical discharge machining (LS-WEDM) is an effective alternative to manufacture intricate shapes with high accuracy in difficult-to-machine materials like TC2 (Ti–3Al–1.5Mn). This paper aims to study the dimensional accuracy and surface quality of TC2 workpiece machined by LS-WEDM based on multiple cuts including rough and trim cuts. First, an orthogonal experiment L16 (54) is designed to evaluate the main influencing factors on surface roughness and machining time. Second, the optimum parametric settings for multiple cuts are designed, and the experimental work has demonstrated that the acute angle convex corners machined by LS-WEDM are accompanied with bending angles and the bending direction is opposite to the wire electrode movement, but the obtuse angle does not appear this phenomenon. Moreover, the wire deflection model based on the unilateral discharge mechanism is built to improve the machining accuracy. In addition, by comparing with the kerf and the surface microstructure of rough and trim cuts, the kerf consistency is improved obviously; the craters, cracks, voids and spherical droplets are gradually becoming much smaller size; the 3D surface parameters including Sa, Sq, Sy and Sz are greatly decreased. Eventually, the elongated craters and the overlapping convex peaks are discovered on TC2 workpiece surface.

Fabrication of 3D Microelectrodes by Combining Wire Electrochemical Micromachining and Micro-electric Resistance Slip Welding

Micromachining, using microelectrodes, is a key technology for manufacturing three-dimensional (3D) microstructures. However, 3D microelectrodes are difficult to fabricate, 3D microstructures are fabricated mainly using simple-shaped tools microelectrode with a layer by layer scanning strategy. Based on micro double-staged laminated object manufacture (micro-DLOM), 3D microelectrodes can be obtained by combining closed loop middle-speed wire (Ø100∼180μm) electrical discharge machining (WEDM) and thermal diffusion welding. But it is difficult to obtain 3D microelectrodes with an edge length of end face less than 100μm, though by low speed wire electrical discharge machining (LS-WEDM) or femtosecond laser cutting, the dimension of 3D microelectrodes can be further miniaturized, they are both very expensive. To solve the problem above, this paper proposed a low-cost method combining wire (Ø8μm) electrochemical micromachining (WECMM) and micro-electric resistance slip welding to fabricate 3D microelectrodes. Firstly, with WECMM combining low frequency micro-vibration and travelling of wire electrode, 30-μm-thick 0Cr18Ni9 stainless steel foils were cut to obtain multi-layer two-dimensional (2D) microstructures. Secondly, through micro-electric resistance slip welding, the multi-layer 2D microstructures were laminated and bonded to fit 3D microelectrodes. Moreover, this paper investigated the influences of applied voltage, feed speed, wire electrode travelling and micro-vibration on machining surface quality and dimensional accuracy. Based on the studies above, two typical 3D microelectrodes with a dimension less than 100μm were successfully fabricated. Finally, applying the fabricated 3D microelectrodes to micro-electrochemical machining (micro-ECM), 3D micro-cavities were obtained.

Study on Finishing Cut with Dry WEDM

Utilizing gas as the dielectric instead of dielectric liquid has enabled the development of dry wire electrical discharge machining (WEDM) technology for finishing cut. This paper studies on the surface quality of tool steel with WEDM method, which is conducted in gas to improve the accuracy of finishing cut, and compares the surface quality in atmosphere and in water. Experiment results showed that Low-Speed WEDM in atmosphere offers advantages such as better straightness, lower surface roughness and shorter gap length, but WEDM in atmosphere has poorer material removal rate than conventional WEDM in water. It was also found the removal rate in atmosphere can be improved by increasing the wire winding speed.